This invention relates to thermal probe systems.
There are several well-known spectroscopy techniques that can be used to make localized infra-red examination of a sample, such as Fourier transform-infrared microspectroscopy and micro-attenuated total reflectance spectroscopy. Recently an alternative technique known as photothermal microspectroscopy has been proposed. This employs a modified form of the probe used in atomic force microscopy to contact and measure the temperature of a localized region on the surface of the sample. The probe employs a small diameter platinum-rhodium wire bent into a V shape with its apex providing the sensing point. As well as sensing the temperature, the probe also acts as a heater to warm the sample where it is contacted. Alternatively, the heating can be achieved by focussing a beam of infrared radiation into a small spot 2 mm in diameter. This can give information about the topography of the sample as well as sub-surface detail resulting from local variations in the thermal conductivity of the sample. Further information about this form of spectroscopy is given in “Mid-infrared Microscopy of Difficult Samples Using Near-Field Photothermal Microspectroscopy” by A Hammiche et al, pps 20-42, Spectroscopy 19(2), February 2004. A problem with this form of spectroscopy is that the noise produced in semiconductor device preamplifiers is high compared with the signal from the probe and makes it very difficult to extract useful information.
It is an object of the present invention to provide an alternative thermal probe system.
According to the present invention there is provided a thermal probe system including a thermal sensing probe and a preamplifier connected with the probe and having an output arranged for connection to an amplifier, the preamplifier including a transformer arranged to increase the signal from the probe.
The system preferably includes a bridge circuit, the probe being connected in an arm of the bridge circuit. The output of the bridge circuit is preferably connected to an input of the transformer. The system may include a voltage source and a plurality of amplifiers connected between the voltage source and resistors of the bridge circuit. The bridge circuit may include adjustable means, such as a potentiometer, for balancing the bridge. The system may include an output amplifier having its input connected with the output of the transformer. The system may include a display arranged to indicate the output of the probe. The probe is preferably a Wollaston thermal sensor. The preamplifier is preferably enclosed within a screened enclosure.
A photothermal system according to the present invention will now be described, by way of example, with reference to the accompanying drawing.